Density Mediates the Predator-Induced Growth and Metamorphic Plasticity of Chinhai Spiny Newt Larvae

Predators significantly influence amphibian larval development. Predator-induced plasticity is often studied independently from conspecific density effects, but these environmental factors may interact. We conducted two-factor factorial experimental design to manipulate conspecific density and predator cues, aiming to investigate the independently or interactive impacts of these two factors on the development of Chinhai spiny newt larvae (Echinotriton chinhaiensis). Our findings reveal that both high and low conspecific densities constrain spiny newt larval growth and predators also limit growth. Interestingly, high conspecific density restricts predator-induced growth plasticity without interacting effects. Only lower density groups exhibit slower growth responses to predators. Our study investigates how density mediates predator-induced plasticity in the endangered Chinhai spiny newt larvae, providing insights into their intricate life history. These results contribute to the understanding of predator-induced plasticity in amphibians and provide insights into the adaptive strategies of endangered species like Chinhai spiny newt. Such knowledge informs the development of effective conservation strategies for their protection.

Legacy effects in temporally separated tadpole species are not mediated by invasive Western Mosquitofish (Gambusia affinis)

Temporally separated species are often thought to have limited competition over a shared resource. However, early arriving species may consume a limited resource such that later-arriving species have access to fewer resources and thus experience competitive effects, even if they are temporally separated (i.e., they experience legacy effects from the early species). The presence of a predator might affect potential legacy effects by influencing the behavior or survivorship of the early species. Using a mesocosm experiment, I examined whether the presence of nonnative Western Mosquitofish (Gambusia affinis) mediated legacy effects in the interaction of two temporally separated species of tadpoles, early arriving American Toads (Anaxyrus americanus) and late-arriving Bullfrogs (Rana catesbeiana). Anaxyrus americanus tadpoles reduced R. catesbeiana tadpole growth despite all A. americanus tadpoles metamorphosing 8 days before the introduction of R. catesbeiana tadpoles into the mesocosms (i.e., legacy effects). Gambusia affinis had limited effects on A. americanus (1 day delay in metamorphosis but no effect on survivorship or size at metamorphosis) and positive effects on R. catesbeiana (increased growth). There were no significant interactions between the A. americanus tadpole density and G. affinis treatments. In conclusion, I found evidence of significant legacy effects of A. americanus tadpoles on R. catesbeiana tadpoles, but no evidence that G. affinis mediated the legacy effects.

The effects of exposure to pyriproxyfen and predation on Zika virus infection and transmission in Aedes aegypti

Zika virus (ZIKV) is an emerging mosquito-borne pathogen that can cause global public health threats. In the absence of effective antiviral medications, prevention measures rely largely on reducing the number of adult mosquito vectors by targeting juvenile stages. Despite the importance of juvenile mosquito control measures in reducing adult population size, a full understanding of the effects of these measures in determining mosquito phenotypic traits and in mosquito-arbovirus interactions is poorly understood. Pyriproxyfen is a juvenile hormone analog that primarily blocks adult emergence, but does not cause mortality in larvae. This mechanism has the potential to work in combination with other juvenile sources of mortality in nature such as predation to affect mosquito populations. Here, we experimentally evaluated the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on Aedes aegypti phenotypes including susceptibility to ZIKV infection and transmission. We discovered that combined effects of pyriproxyfen and Tx. rutilus led to higher inhibition of adult emergence in Ae. aegypti than observed in pyriproxyfen or Tx. rutilus treatments alone. Adult body size was larger in treatments containing Tx. rutilus and in treatments mimicking the daily mortality of predation compared to control or pyriproxyfen treatments. Susceptibility to infection with ZIKV in Ae. aegypti was reduced in predator treatment relative to those exposed to pyriproxyfen. Disseminated infection, transmission, and titers of ZIKV in Ae. aegypti were similar in all treatments relative to controls. Our data suggest that the combination of pyriproxyfen and Tx. rutilus can inhibit adult Ae. aegypti emergence but may confer a fitness advantage in survivors and does not inhibit their vector competence for ZIKV relative to controls. Understanding the ultimate consequences of juvenile mosquito control measures on subsequent adults’ ability to transmit pathogens is critical to fully understand their overall impacts.

Mosquito control approaches primarily depend on lowering the number of potential adult mosquito vectors by inhibiting juvenile stages to reduce the risk of pathogen transmission. Pyriproxyfen is a juvenile hormone analog that inhibits the emergence of adult mosquitoes by interrupting metamorphosis, but does not target larvae. This mechanism allows natural sources of mortality like predation to act in combination with pyriproxyfen to affect mosquito population size. Here, we determined the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on adult Aedes aegypti traits, including infection with Zika virus. Combined effects of pyriproxyfen and Tx. rutilus led to strong inhibition of adult emergence in Ae. aegypti. Treatments containing predators or those mimicking the daily mortality of predation produced larger sized adults. Susceptibility to ZIKV infection was lowest in the predator treatment and highest in the pyriproxyfen treatment. Disseminated infection, transmission, and viral titers of ZIKV were similar between treatments. Our data suggest that the combination of pyriproxyfen and predators can enhance inhibition of adult Ae. aegypti emergence, but survivors may have fitness benefits such being larger mosquitoes. Understanding the consequences of control approaches in mosquito-pathogen interactions will assist to evaluate their suitability in mosquito control programs.